Clamping chuck, notably expansion chuck

ABSTRACT

The invention concerns a clamping chuck in which is embodied a central receptacle ( 4 ) for the shank of a workpiece or tool to be clamped, and a clamping mechanism ( 6 ), a stop element ( 9 ) that can be axially adjusted by means of an adjusting device ( 12 ) being provided for axial positioning of the shank in the receptacle ( 4 ), such that the adjusting device ( 12 ) is configured as a worm gear drive having a worm ( 13 ) rotatably mounted transversely to the receptacle ( 4 ) in the chuck body ( 1 ) and a worm gear ( 14 ) arranged coaxially with the receptacle ( 4 ).

[0001] The present invention concerns a clamping chuck, in particular anexpansion chuck, having a dimensionally stable chuck body in which isembodied a central receptacle for the shank of a workpiece or tool to beclamped, and having a clamping mechanism for securing in the receptaclea shank inserted into the receptacle, a stop element that can be axiallyadjusted by means of an adjusting device being provided for axialpositioning of the shank in the receptacle.

[0002] Clamping chucks of this kind are known in a variety ofembodiments, and are used principally for securing a tool shank, e.g. adrill or milling cutter shank, or also workpieces, in the workingspindle of a corresponding machine tool. For axial positioning of theshank in the receptacle of the chuck body, the known clamping chucksusually have an axial stop which projects from the machine side into thereceptacle and can be moved axially by means of an adjusting device.

[0003] DE Published Examined Application 19 04 536, for example,discloses a clamping chuck in which the axial stop is equipped withexternal trapezoidal threads that are in engagement with trapezoidalthreads of an axially fixed adjusting nut. Rotation of the axial stop isprevented by a pin that engages into a longitudinal groove of the axialstop.

[0004] WO90/10517 furthermore discloses a clamping chuck in which anaxially displaceable, centeredly arranged, and nonrotatable adjustingstem, which is acted upon for axial adjustment by a rotationallyactuated adjusting drive, serves as axial stop for the tool or workpieceto be clamped. The adjusting stem is equipped for this purpose withaxial rack teeth corresponding to a toothed rack, which mesh with anadjusting drive that is embodied as a spur gear and is set tangentiallywith respect to the adjusting stem. A set screw equipped with the stopelement is provided for immobilization of the adjusting stem followingalignment.

[0005] In addition to these clamping chucks in which actuation of theaxial adjusting devices is accomplished from the side in a radialdirection, DE-U 93 01 918.1 discloses a clamping chuck in which theadjusting drive is embodied as a cone that is set obliquely with respectto the longitudinal axis of the axial stop and is equipped on itsconical surface with spiral threads that are in engagement with externalthreads on the axial stop.

[0006] Although the known adjusting devices have proven successful inpractice, it is nevertheless often desirable to be able to perform axialpositioning of the stop element with even greater accuracy andprecision.

[0007] It is therefore the object of the present invention to describe aclamping chuck of the kind cited initially that allows highly accurateaxial positioning of the stop element.

[0008] This object is achieved, according to the present invention,substantially by the fact that the adjusting device is configured as aworm gear drive having a worm rotatably mounted transversely to thereceptacle in the chuck body and a worm gear arranged coaxially with thereceptacle, the stop element being coupled to the worm gear and retainedin the chuck body in such a way that a rotary motion of the worm gear isconverted into an axial motion of the stop element.

[0009] The configuration of the worm gear drive provided according tothe present invention, with a worm and a worm gear meshing therewith,makes it possible to implement any desired reduction ratio of the rotarymotion and thus any desired precision adjustment of the stop elementcoupled to the worm gear. Preferably, a reduction ratio of 1:5 to 1:20can be implemented.

[0010] According to a variant of the invention, provision is made forthe stop element to be retained on the worm gear nonrotatably butaxially displaceably, and to have external threads that are inengagement with internal threads of the chuck body. This configurationmakes it possible, in addition or alternatively to the reduction fromthe worm to the worm gear, to influence the axial adjustment of the stopelement by way of the thread pitches. The greater the thread pitch, themore the stop element moves for each revolution of the worm gear in theaxial direction. This configuration thus makes it possible to achieveparticularly precise setting of the stop element.

[0011] In a development of this embodiment, the stop element can be ofsleeve-like configuration and can be arranged displaceably on a stemthat is connected, in particular detachably, to the worm gear. It isadvantageous in this case if the stem has externally, and the stopelement internally, segments that are in positive engagement with eachother, by way of which the nonrotatable connection between thecomponents is created while retaining axial adjustability of the stopelement. The segments can be embodied, for is example, as internally andexternally hexagonal segments.

[0012] In this embodiment, the worm gear/stem arrangement is preferablymounted in the chuck body by means of a guide bushing, arranged in thechuck body and in particular screwed thereinto, that can additionallycontribute to the axial positioning of the arrangement in the chuckbody.

[0013] According to an advantageous embodiment of the invention, theworm gear/stem arrangement is equipped with a through bore, inparticular arranged centeredly, that provides unimpeded passage ofcoolant to the shank to be clamped.

[0014] According to a further variant of the invention, provision ismade for the stop element to pass through the worm gear and to beretained therein nonrotatably but axially displaceably, and for the stopelement to have external threads which are in engagement with internalthreads of a guide bushing retained in the chuck body. This embodimentpossesses the same advantages as the first variant cited previously, buthas the virtue of making do with fewer components, since an additionalstem is not necessary.

[0015] Regarding further embodiments of the invention, reference is madeto the dependent claims and to the description below of an exemplaryembodiment referring to the appended drawings, in which:

[0016]FIG. 1 shows an embodiment of a clamping chuck according to thepresent invention in a sectioned side view;

[0017]FIG. 2 shows the clamping chuck of FIG. 1 in section along line11-11;

[0018]FIG. 3 shows a further embodiment of a clamping chuck according tothe present invention in a sectioned side view; and

[0019]FIG. 4 shows the clamping chuck of FIG. 3 in section along lineIV-IV.

[0020]FIGS. 1 and 2 depict a clamping chuck according to the presentinvention that is embodied as an expansion chuck. The clamping chuckcomprises a chuck body 1 made of a dimensionally stable material thathas, in a manner known per se, a mounting taper 2 for chucking into areceiving apparatus (not depicted) of a rotationally driven workingspindle of a machine tool. Provided at the other end of chuck body 1 isa connector shaft 3 having a central receiving bore 4 into which theshank (in this case, cylindrical) of, for example, a drilling tool canbe inserted; and a central part 5 of enlarged diameter is locatedbetween mounting taper 2 and connector shaft 3.

[0021] For securing the shank in receiving bore 4, there is depicted inconnector shaft 3 of chuck body 1 an expansion clamping mechanism ofwhich the drawing depicts only a narrow annular chamber 6 that isarranged around receiving bore 4 and oriented coaxially therewith.Annular chamber 6, whose axial length corresponds approximately to thenecessary clamping range, is delimited toward receiving bore 4 by arelatively narrow inner wall 7, and radially externally by an outer wall8 whose wall thickness is several times greater than the wall thicknessof inner wall 7. Annular chamber 6 is filled with a hydraulic mediumsuch as, for example, oil, and communicates (in a manner not depicted)via a conduit configured in chuck body 1 with a hydraulic medium source,by way of which it can have pressure applied to it in order to clamp acomponent. The pressure medium source can be constituted, in a mannerknown per se, by a cylindrical space, configured in chuck body 1, thatis closed off at the end by a piston-like actuating member that can bescrewed into the cylindrical space to elevate the pressure, or screwedout of it to decrease the pressure. This hydraulic pressure istransferred via the conduit to annular chamber 6, and brings about anelastic bulging of inner wall 7 until the latter immovably surrounds ashank inserted into receiving bore 4, and simultaneously a radialbulging of outer wall 8 until the latter lies against the inner wall ofa tool that is set in place.

[0022] For axial positioning of the shank in receiving bore 4, a stopelement 9 is provided which has external threads 10 and is screwed intoa threaded segment 11 of receiving bore 4. Stop element 9 can be rotatedby means of an adjusting device 12 and thereby axially adjusted.Adjusting device 12 is embodied as a worm drive, and comprises a worm 13rotatably mounted in chuck body 1 transversely to receiving bore 4, anda worm gear 14, arranged coaxially with receptacle 4 and connectednonrotatably to stop element 9, that meshes with worm 13. In specific,worm 13, as is readily evident from FIG. 1, is of two-part configurationand comprises a drive screw 15 that is mounted rotatably but axiallyimmovably in a bearing bushing 16 screwed into chuck body 1, the annulargap between bearing bushing 16 and drive screw 15 being sealed by anO-ring 17 to prevent the emergence of coolant, and a worm element 18that is immovably connected (in this case thread-joined) to drive screw15. Drive screw 15 has, at its end facing out of chuck body 1, aninternally hexagonal member 19 for connection with an actuation tool.

[0023] In the embodiment depicted, connection between worm gear 14 andstop element 9 is accomplished by way of a stem 20 that passes axiallythrough worm gear 14 and is nonrotatably connected to it by way of astem/groove connection or the like. On the one side of worm gear 14,stem 20 has a flange-like head 21 that is rotatably mounted and orientedin chuck body 1 coaxially with receiving bore by means of a guidebushing 22 screwed into chuck body 1, the adjusting screw/stemarrangement being positioned axially between guide bushing 22 and ashoulder of chuck body 1.

[0024] On the other side of worm gear 14, stem 20 has a connectionsegment 23 that engages into stop element 9 that is configured insleeve-like fashion, and is connected to it in such a way that stopelement 9 cannot rotate with respect to stem 20 but can be axiallydisplaced. For this purpose, in the embodiment depicted, connectionsegment 23 is configured as an external hexagonal member and the innersurface of the sleeve-shaped stop element 9 is equipped with aninternally hexagonal segment 24, which are in engagement with oneanother.

[0025] In the exemplary embodiment depicted, stem 20 has an axialpassthrough hole 25 through which, during operation, coolant can flowunimpededly to connector shaft 3.

[0026] To adjust stop element 9, worm 13 is turned with a suitable toolsuch as, for example, a socket wrench with hexagonal bit. This rotationof worm 13 is converted, with a reduction ratio of 1:10, into a rotarymotion of worm gear 14 and thus also of stem 20 and of stop element 9nonrotatably connected to stem 20; and the rotary motion of stop element9 results in turn, by way of the engagement of its external threads 10with threaded segment 11 of receiving bore 4, in an axial motion of stopelement 9 which slides on external hexagonal member 23 of stem 20.

[0027]FIGS. 3 and 4 depict a further embodiment of a clamping chuckaccording to the present invention. This clamping chuck possesses thesame basic construction as the clamping chuck depicted in FIGS. 1 and 2,with a chuck body 1 made of a dimensionally stable material that has amounting taper 2 for chucking into a receiving apparatus (not depicted)of a working spindle. Provided at the other end of chuck body 1 is aconnector shaft 3 having a central receiving bore 4 into which the shankof a tool can be inserted. In order to secure the shank in receivingbore 4, there is provided in chuck body 1 an expansion clampingmechanism as has already been described in connection with theexplanation of FIG. 1.

[0028] Axial positioning of the shank in receiving bore 4 isaccomplished by way of a stop element 9 which has external threads 10that are in engagement with internal threads 11 of a guide bushing 22that is screwed into chuck body 1 coaxially with receiving bore 4. Stopelement 9 can be rotated by means of a worm gear drive 12 and therebyadjusted. Worm gear drive 12 comprises a worm 13 rotatably mounted inchuck body 1 transversely to receiving bore 4, and a worm gear 14,arranged coaxially with receptacle 4 and nonrotatably connected to stopelement 9, that meshes with worm 13. Worm 13 has the same constructionas worm 13 of the first embodiment depicted in FIGS. 1 and 2, and toavoid repetition will therefore not be described again.

[0029] Stop element 9 passes through worm gear 14 and is connectedthereto in such a way that it cannot rotate with respect to worm gear 14but can be axially displaced.

[0030] For adjustment of stop element 9, worm 13 is turned with asuitable tool such as, for example, a socket wrench with hexagonal bit.The rotation of worm 13 is converted, with a reduction ratio, into arotary motion of worm gear 14 and thus also of stop element 9. Therotary motion of stop element 9 results in turn, by way of theengagement of its external threads 10 with internal threads 11 of guidebushing 22, in an axial motion of stop element 9.

1. A clamping chuck, in particular an expansion chuck, having adimensionally stable chuck body (1) in which is embodied a centralreceptacle (4) for the shank of a workpiece or tool to be clamped, andhaving a clamping mechanism (6) for securing in the receptacle (4) ashank inserted into the receptacle (4), a stop element (9) that can beaxially adjusted by means of an adjusting device (12) being provided foraxial positioning of the shank in the receptacle (4), characterized inthat the adjusting device (12) is configured as a worm gear drive havinga worm (13) rotatably mounted transversely to the receptacle (4) in thechuck body (1) and a worm gear (14) arranged coaxially with thereceptacle (4), the stop element (9) being coupled to the worm gear (14)and retained in the chuck body (1) in such a way that a rotary motion ofthe worm gear (14) is converted into an axial motion of the stop element(9).
 2. The clamping chuck as defined in claim 1, characterized in thatthe stop element (9) is retained on the worm gear (14) nonrotatably butaxially displaceably, and has external threads (10) that are inengagement with internal threads (11) of the chuck body (1).
 3. Theclamping chuck as defined in claim 2, characterized in that the stopelement (9) is of sleeve-like configuration and is arranged displaceablyon a stem (20) that is connected, in particular detachably, to the wormgear (14).
 4. The clamping chuck as defined in claim 3, characterized inthat the stem (20) has externally, and the stop element (9) internally,segments (23, 24) that are in positive engagement with each other andare embodied in particular as an internally and an externally hexagonalmember.
 5. The clamping chuck as defined in claim 3 or 4, characterizedin that the worm gear/stem arrangement (14, 20) is mounted in the chuckbody (1) by means of a guide bushing (22) provided in the chuck body(1).
 6. The clamping chuck as defined in claim 5, characterized in thatthe guide bushing (22) is screwed into the chuck body (1).
 7. Theclamping chuck as defined in claim 5 or 6, characterized in that theworm gear/stem arrangement (14, 20) is axially positioned in the chuckbody (1) between the guide bushing (22) and a shoulder of the chuck body(1).
 8. The clamping chuck as defined in one of claims 2 through 7,characterized in that the worm gear/stem arrangement (14, 20) isequipped with an axial and, in particular, centrally configured throughbore (25) through which a coolant can be delivered to the receptacle(4).
 9. The clamping chuck as defined in claim 1, characterized in thatthe stop element (9) passes through the worm gear (14) and is retainedtherein nonrotatably but axially displaceably, and the stop element (9)has external threads (10) which are in engagement with internal threads(11) of a guide bushing (22) retained in the chuck body (1).
 10. Theclamping chuck as defined in claim 9, characterized in that the wormgear (14) is axially positioned in the chuck body (1) between the guidebushing (22) and a shoulder of the chuck body (1).
 11. The clampingchuck as defined in one of the foregoing claims, characterized in thatthe worm (13) has on its outwardly directed end means (19) forconnection with an actuation tool.
 12. The clamping chuck as defined inone of the foregoing claims, characterized in that the worm (13) ismounted rotatably and axially immovably by means of a bearing bushing(16) provided in the chuck body (1), the annular gap between bearingbushing (16) and worm (13) preferably being sealed to prevent theemergence of coolant.